Significant research has been conducted in recent years on the use of biological agents to increase agricultural productivity and efficiency. Biological control using microorganisms to suppress plant pests or to supplement plant growth is an attractive alternative to chemical pesticides which are less favored because of concerns about human health and environmental quality. Biological agents effective in the laboratory or in the field to combat pests or facilitate plant growth can be obtained in screening programs.
"Biological control" is defined as suppressing a pathogen using a second organism. Mechanisms of biological control are diverse. For example, certain bacteria can biologically control fungal root rot in alfalfa by competing with the fungi for space on the surface of the alfalfa roots. In contrast, a toxin produced by one species of bacteria may be used to control another species of bacteria that appears as a pathogen. Bacterially produced antibiotics are examples of such toxins. The toxin can be isolated from the species producing it and administered directly, as is the common procedure with penicillin, or the species itself may be administered under appropriate circumstances to produce the toxin in situ. Once identified, such toxins produced by soil-dwelling bacteria may have utility in diverse other areas as antifungal or antibiotic agents.
A biological control agent of scientific and economic significance is Bacillus thuringiensis (Bt). B. thuringiensis strains produce toxic proteins (Bt toxins) that specifically kill certain insects with different strains exhibited variations in target range and efficacy. In addition, methods exist for stabilizing and applying such Bt toxins, or strains harboring them, to a wide variety of field crop situations. Understanding gained by studying B. thuringiensis strains was largely transferable to other strains since toxins required for biological control and methods for preparing inocula for field use can be similar among strains.
A specific Bacillus cereus strain UW85 (ATCC 53522), has biocontrol efficacy in many applications. UW85 protects alfalfa seedlings from damping off caused by Phytopthora medicaginis (Pmm), protects tobacco seedlings from Phytopthora nicotianae, protects cucumber fruits from rot caused by Pythium aphanidermatum, and protects peanuts from Sclerotinia minor. UW85 is also described, by reference to its ATCC number in U.S. Pat. No. 4,877,738. UW85 also produces two compounds having antifungal and antibacterial activity that independently contribute to suppressing damping-off fungi. The more potent of these compounds, a novel aminopolyol is designated zwittermicin A. The second compound is kanosamine, an amino glycoside antibiotic.